1. Field of the Invention
The present invention relates to an apparatus for controlling a reproduction speed for a laser disc player, in which the data recorded on a disc is reproduced while controlling the revolution of the spindle motor by means of driving pulses for the spindle motor.
2. Prior Arts
Generally, in laser discs of a constant linear velocity type, the rotation speed of the spindle motor should be about 1800 rpm in its inner circumference, and about 600 rpm in its outer circumference. Therefore, the recorded amount of data per unit inner track and per unit outer track are different from each other, with the result that it is difficult to control the rotation speed of the spindle motor during the variation of the reproduction speed.
Further, when a laser disc player carries out a low speed reproduction or a high speed reproduction for data in which the audio signals and the video signals are recorded on the laser disc in a standard type of a frequency modulation method, the signals have to be converted into the normal type again, this being a problem.
U.S. Pat. No. 4,864,428 discloses an apparatus for adjusting the reproduction speed for a laser disc player. This patent provides a technique for controlling the rotation speed of the spindle motor of a laser disc player in accordance with the difference in the phase and frequency between reference synchronizing signals and the signals read from the laser disc. FIG. 1 is a block diagram showing the constitution of the reproduction speed adjustable laser disc player of U.S. Pat. No. 4,864,428.
As shown in FIG. 1, in the reproduction speed adjustable laser disc player, a disc 1 is driven by a spindle motor 2, and the data recorded on disc 1 are read by an optical pick-up 3. The audio data which are read by optical pick-up 3 from disc 1 are amplified by a pre-amplifier 4, and then, are supplied to an audio demodulating circuit 5 to be demodulated before being supplied to an audio signal output terminal 6. Meanwhile, the video components are supplied to a video demodulating circuit 7 to be demodulated by it, and are supplied through a video memory 8 to a video output terminal 9. The output of video demodulating circuit 7 are also supplied to a synchronizing signal separating circuit 10 and to a write clock and address generating circuit 11.
Horizontal synchronizing signal separating circuit 10 separates and extracts the horizontal synchronizing signals from the video signals to send them to a spindle servo circuit 12. Spindle servo circuit 12 compares the received horizontal synchronizing signals with a reference signal of the variable frequency which is generated by a variable frequency signal generating circuit 17. The variable frequency reference signal is used as a reference signal in spindle servo circuit 12 which controls the rotation speed of disc 1.
Spindle servo circuit 12 detects the frequency and phase differences between the reference signal and the restored horizontal synchronizing signals so as to generate servo control signals which are varied in accordance with the detected frequency and phase differences. These servo control signals are used for controlling the driving of spindle motor 2 through driving circuit 14, so as to ultimately control the rotation speed of the disc.
In the apparatus of FIG. 1, the video data of disc 1 are stored into video memory 8 in a proper sequence in accordance with the write clocks and the address signals which are generated by write clock and address generating circuit 11 based on the reproduced video signals. The frequency of the video memory reading clocks which are generated by reference signal generating circuit 13 is decided in accordance with the reference signals, and therefore, the video signals which correspond to the television broadcasting standard appear on the video output terminal 9.
As for the audio signals of disc 1, their demodulated output is supplied directly from audio demodulating circuit 5 to audio output terminal 6, and therefore, the pitches of the audio signals are varied proportionately to the rotation speed of the disc.
However, in the spindle motor control method of FIG. 1 in which the speed of the spindle motor is controlled in accordance with the phase difference and the frequency difference between the reference synchronizing signals and the synchronizing signals read from the disc, an exact synchronization is not realized between the audio signals and the video signals, with the result that the picture reproducing speed and the audio reproducing speed do not correspond to each other.
Further, in the case where the reproducing speed is fast, the capacity of the video memory should be larger compared with the normal reproduction, with the result that the manufacturing cost is increased.